The worldwide problem of trafficking of illicit drugs continues despite attempts by enforcement authorities to minimize or eliminate such trafficking. Drug enforcement techniques have become more sophisticated, but traffickers have responded by developing ways to get around presently available enforcement techniques.
One particular area of interest for enforcement agencies is the importation into a country of illicit drugs. Drugs which are transported by air, surface, or vessel are typically concealed by the trafficker in sealed packages, carried on his/her person, in luggage, or in shipments of legitimate cargo. Enforcement agencies are, therefore, in need of a quick and easy-to-use apparatus and method to detect trace amounts of the illicit drugs so that they may be apprehended and seized before entering the country.
Illicit drugs have generally low vapour pressures. They also have another similar characteristic, in that they are often transported in the form of fine granules. These granules are relatively adhering substances. Thus, trace amounts of these granules (particulates) are often present on the clothes of the individuals who have handled the substances, or on the outside of the luggage, or other container in which the illicit drugs are being transported.
Apparatus and methods to detect trace amounts of illicit drugs have been developed over the past decade.
These detection means have been variously based on the use of mass spectrometry (e.g. the work of Sciex, as embodied in U.K. Patent GB 2,162,944B) ion-mobility spectrometry (e.g. the work of Barringer Research Inc., as embodied in the paper entitled "The Detection of Drugs" by John Davies, in Modern Security Systems--A Collection of Papers Presented during International Seminar Held in New Delhi, October, 1989, published by Central Industrial Security Force, New Delhi) and gas chromatography, using a thermionic (nitrogen-phosphorous) ionization detector (TID) as embodied in the article "Portable Trace Narcotics Detector for Field Use", by L. Elias and A. H. Lawrence, Canadian Journal of Spectroscopy, Vol. 32, No. 2, 1987.
Each of these detection means has its intrinsic advantages and disadvantages. For example, mass spectrometry is highly sensitive and discriminating, but ponderous, expensive and difficult to maintain. Ion-mobility spectrometry is sensitive and discriminating, but prone to interferences and contamination and somewhat weighty. GC-TID is sensitive and of reasonable weight and maintenance, but requires the use of a special H.sub.2 /N.sub.2 mixture as carrier gas, and this is not always readily obtainable.
Typically, methods for detecting trace amounts of illicit drugs will include at least three major steps: 1) collection of a sample of particulates, 2) preconditioning of the sample to release vapours characteristic of the illicit drugs, and 3) analysis of the vapours so released, thereby identifying the substances in the sample and determining the amounts present.
The analysis step may entail the use of gas chromatography, ion mobility or mass spectroscopy. We have found the former to be particularly useful for this purpose. The gas chromatograph may be of the "packed column" type or the capillary column type. The latter is preferable as it makes the overall system smaller and more compact. It is well known that the gas chromatograph's column is used to separate the various constituents of the sample based on their respective retention times in the column. A final detector is included in the gas chromatograph to indicate when the individual constituents of interest of the sample exit the gas chromatograph's column. The traditional final detector for the gas chromatograph may be an electron capture detector, a photo ionization detector, a thermionic detector or other suitable detector, depending on the target constituents of interest.
One requirement for using gas chromatography and its associated detector is that a carrier gas must be used. First the sample is vaporized, and the vapour is injected into the flow of carrier gas, which in turn flows through the column of the gas chromatograph and through the detector. The carrier gas, therefore, has to be clean, in the sense that it is free of the substances to be detected, and chosen so that it does not cause any interference with the detection of those substances. Until now, carrier gases have included chemically inert gases, such as helium and argon, or relatively inert gases, such as nitrogen. As well, depending on the type of detector used, mixtures of inert gases with hydrogen may also be used.
For the detection of illicit drugs, particularly cocaine and heroin, thermionic detectors (e.g. Ref. U.S. Pat. No. 4,622,305, Paul L. Patterson, inventor), used with gas chromatographs have proven useful. However, they require a special hydrogen/nitrogen gas mixture as the carrier gas. The cost and availability of this hydrogen/nitrogen mixture and the uncertainties involved in its use and maintenance limit the practical usefulness of thermionic detectors and the portability of the apparatus as a whole. Accordingly, it would be desirable to have a detector that, in conjunction with a gas chromatograph, did not require a hydrogen/nitrogen mixture or other special gas as a carrier gas. A detector that can be used when ambient air is used as the carrier gas is highly preferable.